1. Field of the Invention
The invention relates to a process for the recovery and recycle of the organic binder components which accumulate during the spraying of one- or two-component, solvent-containing polyurethane coatings.
2. Description of the Prior Art
State of the art two-component, solvent-containing polyurethane coatings have gained great practical importance in the coatings sector because of their outstanding properties. In practice, the coatings are generally applied by spraying onto the substrate to be coated. In this process, the loss of significant amounts of the binder components used, due to "overspray," cannot by avoided. In practice, these excess amounts are generally washed out of the vent gases in the coating unit using water and coagulated by the joint application of coagulating agents, e.g., surface-active inorganic materials such as alumina. Previously, it has not been possible usefully to recycle this "coatings slurry."
Therefore, an object of the present invention is to develop a process for recovering and recycling the binder components present in the coatings slurry before they have become completely unusable due to the gradual and progressive cross-linking reaction. It is a further object of the present invention for the process to be also suitable for treating solvent-containing, one-component polyurethane coatings having binders based on moisture-hardening NCO prepolymers.
It has now been found that the organic binder components may be extracted from the fresh coatings slurry containing
a) organic polyisocyanates PA1 b) (in the case of two-component polyurethane coatings) organic compounds with groups capable of reacting with isocyanate groups, preferably organic polyhydroxy compounds, PA1 c) optionally pigments and/or other auxiliaries and additives, PA1 d) coagulating agents and PA1 e) water, PA1 i) forming a coatings slurry containing the organic binder components, water and a coagulating agent, PA1 ii) mixing the coatings slurry, optionally after removing a portion of the water, with an organic solvent which is inert towards isocyanate groups, PA1 iii) reacting the free isocyanate groups present in the mixture obtained in step (ii) with a compound containing one isocyanate-reactive group which is more reactive with isocyanate groups than both water and the isocyanate-reactive component of the two-component polyurethane coating, if present, and PA1 iv) removing any remaining water and insoluble components from the organic phase accumulating in step (iii) and recovering the organic phase containing the organic binder components.
if the coatings slurry is initially introduced into an organic solvent and then reacted with compounds which are more reactive with isocyanate groups than both water and the reaction partner which contains isocyanate-reactive groups.